The objective of the proposed experiments is to obtain cell kinetic information on the EMT-6 tumor system in vivo, using traditional 3H-thymidine autoradiography and a new method for determining growth fraction, the PDP (template-primer available, DNA-polymerase-containing nuclei) technique. This will be combined with data on clonogenic cell survival, determined by colony forming ability in vitro, after treatment in vivo with drugs or radiation plus drugs. The drugs to be studied include cyclophosphamide, bleomycin, actinomycin D, and cytosine arabinoside. The specific problems to be examined include: relative drug sensitivity of cells in small and large primaries and in metastases, relative to the cell kinetics of each; clonogenicity and drug sensitivity of proliferating and nonproliferating cells in large tumors; role of radiation-damaged tumor circulatory system in determining reduced growth rate and drug delivery in tumors recurring after X-rays; and recruitment of nonproliferating cells by fractionated X-irradiation, to be followed by chemotherapy.